Bob Moler's Ephemeris Blog

Monday, September 27th.*  The sun will rise at 7:35.  It’ll be up for 11 hours and 55 minutes, setting at 7:30.   The moon, 3 days before last quarter, will rise at 9:16 this evening.

Astronomers have been discovering planets around other stars for the last 15 years.  These planets tend to be as massive as Jupiter or greater, and tend to be very close to their parent stars.  The orbital period of these planets tend to be the matter of days.  Over the years we had been comfortable with how the planets are located in our solar system:  Inner rocky worlds and farther out large gaseous planets.  Now, what we are finding is in part the result of the techniques we use, which are most sensitive to large planets orbiting close to their stars.  Currently aloft is a spacecraft called Kepler that we hope is also sensitive to small planets orbiting farther from their stars by recording them passing in front of their stars.

*Times are for the Grand Traverse Area of Northern Michigan, USA.

Ephemeris for Friday, September 24th.*  The sun will rise at 7:31.  It’ll be up for 12 hours and 4 minutes, setting at 7:36.   The moon, 1 day past full, will rise at 7:43 this evening.

Jupiter is the bright star-like object in the east and southeast in the evening.  In telescopes and even in binoculars the observer can spot up to four stars nearby.  These aren’t stars, but moons or satellites of Jupiter.  Galileo discovered them 400 years ago with his small telescope.  Jupiter has 63 satellites in all, but the rest are tiny objects.  Of the four ‘Galilean’ satellites all but one is larger than the moon.  They are, in order from Jupiter Io, a volcano riddled world which is constantly resurfacing itself.  Next is Europa an icy moon with a good probability of a salty ocean beneath.  Giant Ganymede is next, larger than Mercury, it is also icy with the possibility of an ocean.  Last is Callisto a dark moon with bright craters.

*Times are for the Grand Traverse Area of Northern Michigan, USA.

Ephemeris for Thursday, September 23rd.*  The sun will rise at 7:30.  It’ll be up for 12 hours and 7 minutes, setting at 7:38.   The moon, at full today, will rise at 7:21 this evening.  It’s the Harvest Moon.

Jupiter is the largest planet.  It’s volume could contain 1,300 earths.  It however is only 318 times the earth’s mass.  Still, Jupiter contains the mass of two and a half times all the other planets put together.  Jupiter is basically a huge ball of hydrogen.  It has a rocky/metallic core several timed the size of the earth.  Above that is hot liquid metallic hydrogen to generate Jupiter’s incredibly strong magnetic field.  Above that is a deep ocean of liquid hydrogen that gradually becomes the hydrogen atmosphere.  What we see of the face of Jupiter are clouds of methane and ammonia.  Jupiter doesn’t rotate as a solid body.  It rotates faster at the equator than the poles.  Astronomers have reduced this to three rotational periods, the shortest is less than 10 hours.

*Times are for the Grand Traverse Area of Northern Michigan, USA.

Ephemeris for Wednesday, September 22nd.*  The sun will rise at 7:29.  It’ll be up for 12 hours and 10 minutes, setting at 7:39.   The moon, 1 day before full, will set at 7:51 tomorrow morning.  |  Lets take a look at the bright planets for this week. Venus and Mars are very low in the twilight.  Venus is the brightest.  It’s 40.3 million miles away and slowly approaching, and appears as a thin crescent.  It will set at 8:34 p.m. Mars is right and above Venus, and much dimmer.  I doubt if you could spot it.  The planet Jupiter is up at sunset and will move due south at 1:30 a.m..  It’s located in Pisces this year.  Mercury is visible low in the east before sunrise.  It will rise tomorrow morning at 5:53 a.m.  Mercury is visible in the morning twilight in the east.  6:30 to 7 a.m. is the best time to spot it.  Tonight at 11:09 p.m.  the sun will cross the celestial equator heading south.  For us in the northern hemisphere autumn will begin.

*Times are for the Grand Traverse Area of Northern Michigan, USA.

Ephemeris for Tuesday, September 21st.*  The sun will rise at 7:28.  It’ll be up for 12 hours and 13 minutes, setting at 7:41.   The moon, 2 days before full, will set at 6:49 tomorrow morning.

The planet Mercury is a mysterious place.  It is the closest planet to the sun.  It’s really close now because it’s at its closest part of the elliptical orbit of the sun.  Mercury’s distance from the sun today is 28.6 million miles, and it’s 91.2 million miles from us.  Being the closest planet from the sun has made it very difficult to study with a telescope.  It’s always close to the horizon where the atmosphere raises havoc with the image, and is never visible out of twilight, at least for observers north of the earth’s equator.  It’s a hard planet to get to as seen by the MESSENGER’s long travel time of nearly seven years.  That’s near an end.  In six months MESSENGER is to enter orbit of Mercury.  We’ll get exquisite images and data from this elusive planet.

*Times are for the Grand Traverse Area of Northern Michigan, USA.

Ephemeris for Monday, September 20th.*  The sun will rise at 7:27.  It’ll be up for 12 hours and 16 minutes, setting at 7:43.   The moon, 3 days before full, will set at 5:48 tomorrow morning.

Yesterday Mercury was at it greatest angular separation from the sun.  It is now best seen between 6:30 and 7 a.m. low in the east.  Over the next week it will move back a bit toward the sun and will actually get brighter and its illuminated face gets wider, as its phase increases from half  illuminated to gibbous.  It looks very tiny in telescopes.  Farther from the sun the giant planet Jupiter will appear opposite the sun in the sky, rising at sunset.  Jupiter is that bright ‘star’ seen in the east and southeastern sky in the evening.  Today it is at its closest to the earth.  Because Jupiter is 5 times the earth’s distance from the sun, subtracting the earth’s solar distance from Jupiter; it will be 4 times the earth-sun distance or 368 million miles away.  We’ll visit Jupiter later this week.

*Times are for the Grand Traverse Area of Northern Michigan, USA.